Manufacture of nitriles



- Oct. 10, 1950 -rs 2,524,831

MANUFACTURE OF NITRILES 2 Sheets-Sheet 1 Filed on. 17 1945 wrzaezzser'35 Nllfl z I 2 Feed awe/L Me:

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1950 R. H. POTTS 2,524,831 MANUFACTURE OF NITRILES FiledOct. 17, 1945 2Sheets-Sheet 2 "H3 'V Cords/war 20 em;

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Ea lph H. Potts Patented Oct. 1 0, 1950 2,524,831 r V p MANUFACTURE orNITRILES Ralph H. Potts, La Grange, IlL, assignor to Armour and Company,Chicago, 111., a corporation of Illinois Application October 17, 195,Serial No. 622,925

This invention relates to the preparation of fatty acid nitriles anddeals especially with continuous processes for preparing such nitriles.

The nitriles of the higher fatty acids, namely those fatty acids havingeight or more carbon atoms, are substances of increasing technicalimportance. They are useful in the arts as such, and they can be readilyhydrogenated to corresponding primary aliphatic amines.

An important object of the present invention is to provide simple andeffective processes for conducting the reaction of fatty acids andammonia to produce the corresponding nitriles. Another object is toprovide such processes which may be easily and economically operatedwith a minimum of equipment to produce the desired products at a rapidrate. Another object is to provide processes which can be continuouslyop- Figure 1 of the accompanying drawing is a schematic diagram of onetype of apparatus which may be used in carrying out the improvedprocesses. It is understood, however, that widely differing types ofequipment may be used in practicing the invention. a

In the apparatus illustrated in Figure 1, the fatty acid feed enters atower arrangement 20 by way of line 2|. This tower is equipped withreceptacles consisting of bubble trays and plates. Any suitable numberof trays may be used and the tower may be of any suitable size andheight. The tower can be looked upon ascontaining three general zones.That zone disposed at about the middle of the tower is the reaction zonewherein the primary reaction between ammonia and the fatty acid takesplace. The upper section of the tower can be considered as therectifying zone wherein nitriles are continuously separated from fattyacids, and the lower or stripping zone is the section where fatty acidsare separated from amides. Ammonia enters the tower through line 23,amide may be withdrawn through line 24, and vapors leave the towerthrough line 25 to a condenser 26 wherein the nitrile product iscondensed. Arrangementis made for the return of reflux, if desired,through line 21 connecting with nitrile, outlet 28. 'As here shown themoisture and excess ammonia pass off through vent 26a to the atmosphere.If desired, provision can be made for recovering the excess ammonia forre-use in the process.

The middle section or reaction zone of the tower is heated with one ormore heating coils schematically shown at 29. These heating coils aredesirablyheatedwith a fluid which is introduced in the vapor-state buthas a condensation temperature above the reaction temperature to bemaintained in the reaction zone. Such a fluid may suitably be a, mixtureof diphenyl and diphenyl oxide. Other ways of heating the reaction zonecan beused, for example, the heating coils 29 can contain steam as aheating fluid, or electrical heating'elements can be employed.

The following detailed description of the operation of this arrangementillustrated will deal with the. reaction of stearic acid for purposes ofexplanation, it being understood that other suitable stock maybe used inplace of this.

The liquid stearic acid after being passed throughline 2| into the towermeets an upward current of ammonia, and .here enters into reaction withammonia. It is believed that thereactlon involves first the formation ofammonium soaps (RCOO'I-I+NH3 RCOONH4); the soaps then breaking down toform stearamide and water (RCOO'NH4+RCONH2+H2O) and the amide thenbreaking down to form nitrile and ammonia and fatty acid The nitrilesboil at lower temperatures than the corresponding fatty acids and thefatty acids boil at lower temperatures than the corresponding amides.

The liquid acid which is passed through line 2| into the tower isdischarged on the tray 60 intothe liquid p001 held on this tray. As itoverflows tray 60, the stock falls to tray 6| into a secondpool andthence to tray 62 into a third liquid pool, and so on through thereaction zone. Gaseous ammonia is continuously passing upwardly throughthe reaction zone and is caused to pass successively through the. liquidpools on trays 64, 63, 62, El, and 60. Contact of ammonia with liquidacid on tray 64 at the temperature maintained in the reaction zoneresults in reaction of ammonia and acid to produce nitriles which atthis temperature vaporize and pass upwardly along with reacted ammonia.Likewise in the pool on tray 63 further reaction of liquid acid andammonia takes place to produce further nitriles which vaporize and alsopass upwardly along with excess ammonia. Likewise in'each'of pools 62,BI and 60 further reactionresults in the production of furtherquantities of nitriles which vaporize after their formation. In thisoperation the vaporous nitriles formed as a result of the reaction inthe lower pools of the series pass through each of the'pools above andin doing so provide violent agitation of the material still in liquidphase and greatly increasedispersion of ammonia in the pools throughwhich these vaporous nitriles pass, thus-promoting better contactbetween the reactants in'these higher pools.

The vaporous nitriles passing upwardly from tray 60 atthe upper portionof the reaction section enter the rectifying section; Some fatty acidswill unavoidably be entrain-ed or vaporized and will pass upwardly alongwith the vaporous nitriles into the rectifying zone. In the rectifyingzone are a second series of zones containing pools of liquid. As shownin Figure 1, reflux liquid in the form of condensed nitriles isintroduced at the upper portion of the rectification zone. As the vaporsfrom the reaction zone, including nitriles and some fatty acids, passupwardly through the pools of liquid counter to the reflux nitriles, thefatty acids, being of higher boiling point than the nitriles, areselectively condensed, and the vapors reaching the top of the rectifyingzone are substantially pure nitriles. The pools within this zone will befound to contain a successively larger proportion of nitriles and asmaller proportion of fatty acids toward the upper portion of the zone.Any acids which have been carried up from the reaction zone will bequickly condensed and returned to the reaction zone by the rectifyingaction. The nitriles proceeding toward the top of the zone finally passoff through line in vaporous form.

The vapcrous nitriles, after being condensed by the condensing equipment26, are recovered in part as a liquid nitrile product and in partreturned through line 21 to the upper portion of the tower as refluxliquid.

As before stated, the reactions taking place at the reaction zone of thetower include the formation of amides, and not all of the amid-esimmediately break down into nitriles, the ratio of amides, nitriles andfatty acids existing in the reaction zone depending in part on thetemperature and the time in contact with the heat supply. The amides,being of higher boiling point than either the corresponding nitriles orfatty acids, will tend to move downwardly in the pools within the tower.The amides, however, are intermixed with unreacted fatty acids, nitrilesand any other high boiling substances of the feed stock; and as thismixture, principally amides and fatty acids, moves into the pools withinthe stripping section against the upwardly moving current of ammonia,the fatty acids and any nitriles present are stripped from the amides.Also, any fatty acids and nitriles formed by further breakdown of theamides are carried upwardly in the same way. Thus the pools within thestripping section contain a successively larger proportion of amides anda smaller proportion of fatty acids toward the bottom of the section. I

The amides collect in substantially pure form' at the bottom of thetower and may be withdrawn either continuously or at intervals throughthe outlet 24. An automatic level regulating device 3! of any suitabletype may be used to maintain a desired level of liquid amide at thebottom of the tower. A heat coil is provided at the bottom of the towerfor supplying heat to the stripping zone in addition to that furnishedfrom the reaction zone where such additional heat is necessary tomaintain the desired temperature. The temperature in the stripping zoneneed only be high enough to vaporize fatty acids in the presence of theintroduced ammonia. The ammonia entering the bottom of the tower causesfatty acid to be vaporized at a lower temperature than would ordinarilyhappen if no ammonia were present. In the stripping zone of the towerthe temperature, for stearic acid nitrile formation, is maintained at anaverage of about 300 C. which is high enough to cause the stearic acidto boil without vaporizingthe stearamide. Under the conditions of theprocess, having regard for the introduction of ammonia and its tendencyto lower the boiling points of the fatty acid materials in the tower,the stearic acid will boil at 297 C. whereas stearamide boils at 321 C.

Temperatures maintained within the tower are, of course, dependent uponthe kind of fatty acid introduced. With stearic acid the reactionheaters 29 may be maintained at a temperature of about 300 C. This isbelow the boiling point of stearic acid at ordinary room pressure in theabsence of any added ammonia. In view of the ammonia present, however,some of the stearic acid will vaporize before it has reacted withammonia to form ammonium soaps as a. first product. The upper section ofthe tower may be maintained at about 275 C. which is low enough to causethe stearic acid vapors in the rectifying zone to condense but is highenough to maintain the nitrile in the vapor state. Thus, there is acontinuous rectification of the mixture of nitrile vapors and stearicacid vapors entering the rectifying zone and the stearic acid is pusheddown from the rectifying zone into the reaction zone.

As above indicated, there will also. be a temporary accumulation ofstearic acid amide in the reaction zone. This amide, together withunreacted fatty acid flows downwardly into the stripping zone maintainedat a temperature of about 300 C., for example. As before stated, underthese conditions fatty acid accumulated in the stripping zone is pushedupward into the reaction zone leaving thestearamide behind. Thus, thisprocess permits the continuous production of both nitriles and amides.

However, when nitrile only is the desired prodnot then the outlet at thebottom of the tower can be closed. Amide collection in the strippingzone decomposes continuously to form nitrile and fatty acid inaccordance with the equations before given, and both of these substancespass into the reaction zone, with the nitrile finally passing from therectifying zone and out of the tower. In this case the tower acts as anitrile production unit without the recovery of an amide product. Theamide collects at the bottom of the tower where it is built up to suchextent that its conversion into nitriles by decomposition isautomatically accomplished.

It will be observed that when nitriles only are produced, the strippingzone serves no useful purpose; consequently where amides are not desiredthis section may be omitted.

The rectifying, reaction and stripping sections may of course take formswidely differing from that shown in Figure 1, and, if desired, thesesections may be disposed indifferent enclosures or towers instead of ina single tower as shown.

A modified type of reaction section is illustrated schematically byFigure 2 of the drawings in which is contained the trays 35 whichprovide a series of intermediate zones comprising liquid pools. Liquidis withdrawn from the lower portion of the section through line 35 bythe pump 3'! and passed through the heater 38 and returned to the upperportion of the section through line 39. The heater may emplo as aheating medium a mixture of diphen-yl and diphenyl oxide which condensesat the temperature desired to be maintained. Of course other suitableheating means may be employed. In the operation of this modifiedarrangement the liquid within the reaction zone is passed downwardly inconsiderable volume due to the circulation here provided,

5. and this enables very efficient contact between the'liquid and theupwardly moving ammonia.

With other fatty acids the process may be the same, although the towertemperature conditions will vary to meet the requirements of anyparticular acid. These requirements are simply that the reaction zone beoperated at a temperature such that nitriles are distilled from thereaction mixture, the stripping zone be operated at a temperature suchthat fatty acids are vaporized, in the presence of the added'ammonia,and the rectifying zone be operated at such a temperature that fattyacid vapors are substantially condensed therein while at the same timedelivering the nitriles in vaporous form.

The reaction taking place within the reaction zone is substantially inthe liquid phase, although because of the presence of ammonia there willbe some vaporization of fatty acid. The vaporized fatty acid, however,is condensed in the rectifying section and so returned in liquid phasefor reaction with ammonia in the reaction zone.

It is essential that the ammonia passing into the reaction zone be inexcess of the amount stoichiometrically required by theory for reactionwith the feed stock being introduced. For good operation the amount ofthe ammonia should be at least two times the theoretically requiredamount, and preferably about five times the theoretically'requiredamount.

The feed stock may be any higher fatty acid such as stearic, palmitic,oleic, linoleic, lauric, etc. or mixtures of such acids such as thenatural fatty acid mixtures obtained upon hydrolysis of natural oilssuch as soyabean, cottonseed, tallow or fish oil. Also, I may use rosinacids such as the rosin acid contained in tall oil, or I may use thefatty acid mixture obtained from tall oil, or tall oil itself. However,it is preferable that the fatty acid-bearing constituents of the feedstock have a rather narrow range of boiling points so that the nitrileof one constituent will not be held with the fatty acid or amide ofanother constituent to an objectionable degree as the process goesforward.

I have found that a particularly suitable feed material is produced byhydrolyzing some naturally occurring oil, such as soyabean oil orcottonseed oil, and then fractionating the acids so obtained accordingto the processes set forth in the Potts et al. Patent No. 2,224,984 toproduce a fraction containing a high proportion of acids which boilwithin a narrow range. I

While in the foregoing description and illustration the rectifying,reaction, and stripping sections employed have been, for clearness ofunderstanding, set out as distinct and permanent sections, it must beunderstood that there may be considerable overlapping of the parts ofthe equipment which serve as such sections. For example, using one typeof stock and one set of temperature conditions, the respectivereactions, stripping, and rectifying functions may be taking place atcertain positions within the tower, while with some other stock andusing other conditions these functions and reactions may take place atother points. Thus, when -I refer to a reaction section, for example, Imean to indicate the portion wherein the reaction takes place under theconditions of operation employed, and not necessarily a precise part ofa tower.

Figure 3 of the drawings shows schematically a modified type ofapparatus wherein the rectifying section employed in Figure 1 has beenreplaced by a catalyst chamber. As here shown,

shown in Figure l.

the tower 40 is provided with trays 41, similar to those in theapparatus previously described. Leading from the reaction section of thetower is a conduit 42 which connects with the catalyst chamber 44.

Th catalyst chamber 44 here shown is formed of a plurality of tubes 45,the ends of which communicate with the heads 46 and 41. Held withinthese tubes is a suitable dehydrating catalyst such as alumina. Forheating this catalyst chamber a suitable heating fluid such as a mixtureof diphenyl and diphenyl oxide is introduced in a vaporous form into thespace about the tubes through the inlet 48, and then withdrawn in liquidform through outlet 49. Other types of catalyst chambers may, of course,be used.

In the operation of this modified system, the fatty acid stock isintroduced through pipe 50 into the tower 40 where it passes downwardlythrough the series of zones against an upwardly moving current ofammonia just as in the system Here a substantial reaction takes placebetween the acids and ammonia which yields a mixture including nitriles,amides, water and unreacted fatty acids. As heat is absorbed the waterand nitriles are rapidly vaporized and passed out through the conduit42, and since no substantial rectification takes place a certain amountof fatty acids and amides may also be carried along with the nitrilesall in vaporous form. When this vaporous mixture enters the catalystchamber 44 and comes into contact with the catalyst, any unreacted fattyacids and the amides are converted to nitriles. By means of the heatingfluid the catalyst chamber'is maintained at a suitable temperature forliquid phase reaction such as 600 F. e

The temperature of the reaction zone at tower 40 should be above theboiling points of the nitriles under the pressure conditions employed,but should be below 700 F. and preferably below 600 F.

The nitrile vapors passing from chamber 44 are condensed by the nitrilecondenser 5| and the moisture and excess ammonia pass off to theatmosphere. As in the first system described, suitable arrangement maybe made for recovering the excess ammonia for re-use in the process.

Where amides are not desired as a by-product, the lower or strippingsection of the tower serves no useful purpose and may be eliminated asmentioned in connection with the first described system.

This system illustrated in Figure 3 is not affected substantially byusing a feed material which contains fatty acid radicals of a wide rangeof boiling points, and so may be preferred for some types of feed stock.For example, the modified system may be efficiently operated using thefatty acid mixtures obtained by the hydrolysis of any natural oil.

The foregoing detailed description has been given'for purposes ofexplanation only and no unnecessary limitation should be understoodtherefrom it being understood that many changes may be made in themanner of carrying out the invention, all within the spirit of theinvention.

This application is a continuation-in-part of my co-pending application,Serial No. 384,232, filed March 20,- 1941, entitled Manufacture ofNitriles, etc., now abandoned.

I claim:

1. In a process for making high molecular weight fatty acid nitriles,the steps of continuously passing fatty acid having at least 8 carducenitriles, vaporizing from said zone a mixture of nitriles and unreactedfatty acid, passing said mixture into a rectifying zone, vaporizing andremoving nitriles from said rectifying zone, condensing fatty acidswithin said rectifying zone and returning condensed fatty acid to saidreaction zone, and subjecting said returned acid to contact in saidreaction zone with a current of ammonia in an amount sufficient forreaction with all said returned acid and all other acid being passedinto said reaction zone to produce nitriles therefrom.

9. In a process for making high molecular weight fatty acid nitriles thesteps of continuously passing fatty acid having at least 8 carbon atomssuccessively through a series of pools of liquid containing fatty acidand nitriles, continuously passing gaseous ammonia through said seriesof pools and into contact with acid in each pool of said series, saidammonia being introduced in an amount of about five times thatstoichiometrically required for reaction with the fatty acid beingintroduced, and maintaining said pools at a temperature sufficient forliquid phase reaction of the acid and ammonia to produce nitriles.

10. In a process for making high molecular weight rosin nitriles thesteps of continuously passing rosin acid having at least 8 carbon atomssuccessively through a series of pools of liquid containing rosin acidsand nitriles, continuously passing gaseous ammonia through said seriesof pools and into contact with acid in each of the pools of said series,said ammonia being in excess of the amount stoichiometrically requiredfor reaction with said acid being introduced, and maintaining said poolsat a temperature sufilcient for liquid phase reaction of the acid andammonia to produce nitriles.

11. In a process for making high molecular weight fatty acid nitriles,the steps of continuously passing a fatty acid fraction having at least8 carbon atoms and consisting of acids having substantially the sameboiling points into a reaction zone, bringing said acid fraction whilein liquid phase into contact with ammonia in said reaction zone whilemaintaining said zone at a temperature sufficient for reaction of saidacid fraction and ammonia to produce nitriles therefrom, vaporizingnitriles so formed and passing the vaporized nitriles together withquantities of vaporized acids upwardly into a rectifying zone containinga series of zones containing successively increasing proportions ofnitriles and decreasing proportions of acids whereby the nitriles arerectified and removed as vapor and fatty acids are returned to saidreaction zone.

12. In a process for making high molecular weight acid nitriles, thesteps of continuously passing acid having at least 8 carbon atomssuccessively through a series of pools of liquid containing said acidand nitriles, said acid being selected from the class consisting ofrosin acids and fatty acids, continuously passing gaseous ammoniathrough said series of pools and into contact with acid in each of thepools of said series, said ammonia being in excess of the amountstoichiometrically required for reaction with said acid, and maintainingsaid pools at a temperature sufiicient for liquid phase reaction of theacid and ammonia to produce nitriles.

13. In a process for making high molecular weight carboxylic acidnitriles from acids selected from the class consisting of rosin acidsand fatty acids, the steps of passing said acids,

having at least 8 carbon atoms, into a zone coritaining a series ofvertically-spaced liquid pools of said acids, amides and nitriles,continuously passing gaseous ammonia through said series of pools andinto contact with said acid in said pools, maintaining said zone at atemperature for liquid phasereaction of acid and ammonia to produceamides and for converting amides to nitriles, passing nitriles upwardlyand amides downwardly in said series of pools, vaporizing and removingnitriles from the uppermost of said pools substantially as rapidly asnitriles are formed in said zone, and retaining within the lower portionof said zone the amides passed downwardly in said series of pools untilsaid amides are decomposed to form nitriles.

14. In a process for making high molecular weight carboxylic acidnitriles from acids selected from the group consisting of rosin acidsand fatty acids, the steps of introducing such acids, having at least 8carbon atoms, into a zone containing a series of vertically-spacedliquid pools of said acids, amides and nitriles, continuously passinggaseous ammonia through said series of pools and into contact with saidacid in said pools, reacting said ammonia and acids to form amides,heating said amides to form nitriles, passing nitriles upwardly throughsaid pools and amides downwardly in said series of pools tosubstantially segregate the amides in the lower pools, and subjectingthe amides in pools to heat to convert the same to nitriles.

15. In a process for making high molecular weight fatty acid nitriles,the steps of continuously bringing fatty acids and ammoniainto contactwithin a, reaction zone under temperatures which produce amides andnitriles, continuously withdrawing nitriles from said zone, continuouslypassing amides formed in said reaction zone downwardly into a secondzone, which is free of nitriles except for those produced in said secondzone by the conversion of amides to nitriles, and subjecting saidsegregated amides in said second zone to the action of heat for theconversion of said amides to nitriles.

16. In a process for makin high molecular weight fatty acid nitriles,the steps of continuously bringing fatty acids and ammonia into contactwithin a, reaction zone under temperatures which produce amides andnitriles, continuously withdrawing nitriles from said zone, continuouslypassing amides formed in said reaction zone downwardly into a secondzone which contains a greater proportion of amides and a lesserproportion of nitriles than said first zone, and subjecting the amidesin said second zone to the action of heat for the conversion of saidamides to nitriles. RALPH H POTTS REFERENCES CITED The followingreferences are of record in the -file of this patent:

UNITED STATES PATENTS

1. IN A PROCESS FOR MAKING HIGH MOLECULAR WEIGHT FATTY ACID NITRILES,THE STEPS OF CONTINUOUSLY PASSING FATTY ACID HAVING AT LEAST 8 CARBONATOMS SUCCESSIVELY THROUGH A SERIES OF POOLS OF LIQUID CONTAINING FATTYACID AND NITRILES, CONTINUOUSLY PASSING GASEOUS AMMONIA THROUGH SAIDSERIES OF POOLS AND INTO CONTACT WITH ACID IN EACH OF THE POOLS OF SAIDSERIES, SAID AMMONIA BEING IN EXCESS OF THE AMOUNT STOICHIOMETRICALLYREQUIRED FOR REACTION WITH SAID ACID, AND MAINTAINING SAID POOLS AT ATEMPERATURE SUFFICIENT FOR LIQUID PHASE REACTION OF THE ACID AND AMMONIATO PRODUCE NITRILES.